Mono- and dialkyltin oxides are industrially of great value and are being used in large quantities in the productions of stabilizers for polyvinyl chloride resins, catalysts for organic syntheses and catalysts for cationic electrodeposition coating, whereas bis(trialkyltin) oxides or trialkyltin hydroxides (hereinafter, both being put together and referred to as "trialkyltin oxides") hold an important position in the field of antifouling paints. So far, these alkyltin oxides have been produced generally by the method as described, for example, in U.S. Pat. Nos. 2,718,522 and 3,390,159. That is, an alkyltin halide is batch-wise hydrolyzed with a strongly basic substance, such as an alkali metal hydroxide or ammonium hydroxide, in the presence of an organic solvent, thereby to form two phases composed of an aqueous phase containing salts and, in some cases, an alkali metal salt of a monoalkyltin oxide and an organic phase containing a di- and trialkyltin oxides, subsequently the organic phase is separated from the aqueous phase, and then the di- or trialkyltin oxide is isolated from the organic phase by mechanical means, such as filtration or centrifugation.
However, such production process has serious problems from the viewpoints of worker's safety and health, environment, and economical production equipment. That is, the dialkyltin oxide is present in the organic phase in the form of very finely dispersed particles generally having an average particle diameter of 10 .mu.m or less and, further, these particles are easily compressed with application of pressure thereon, whereby independence of the particles is destroyed. Hence, the isolation of such dialkyltin oxide takes a long time if performed by a pressure-utilizing means, such as filtration or centrifugation, and causes a very large amount of the solvent or the trialkyltin oxide to be vapolised during the isolation. For example, in the case of the production of a trialkyltin oxide, since the corresponding dialkyltin oxide is formed as a by-product in the form of very minute particles suspended in the resulting liquid trialkyltin oxide, removal of the dialkyltin oxide can be completed only by the use of a filter aid such as acid clay. Further, the dialkyltin oxide thus separated cannot be reused as it is because the filter aid is contained therein, and disposal of the oxide as an industrial waste is difficult. On the other hand, since the aqueous phase containing a monoalkyltin oxide and a salt is difficult to be completely separated from the trialkyltin oxide phase, part of the trialkyltin oxide unavoidably mingles in the aqueous phase and should be removed by extraction with an organic solvent. Moreover, because the adverse influences of trialkyltin oxides on humans and the environment cannot be negligible, the whole manufacturing process should be enclosed in a closed-system. However, a completely enclosed manufacturing process in a closed-system cannot be obtained. Furthermore, the filtering or centrifugial equipment used in the prior art process costs too much.
In the case of di- or monoalkyltin oxides, the conventional production processes have, in principle, the same disadvantages as mentioned above for the case of trialkyltin oxides, but the situation is more complicated since solids are processed in large quantities in the production of di- or monoalkyltin oxides. More particularly, the hydrolysis of a dialkyltin dihalide results in the formation of two phases, namely an aqueous phase containing the corresponding monoalkyltin oxide and an organic phase containing the corresponding tri- and dialkyltin oxides, and then the desired dialkyltin oxide is separated from the organic phase by centrifugation or filtration, or other suitable means. For removing the by-product trialkyltin oxide from the separated dialkyltin oxide, the dialkyltin oxide is washed by suspending it in a solvent and then recovered by filtration or centrifugation, and this procedure is repeated several times. However, in order to completely remove the by-product salt and an alkali metal salt of the monoalkyltin oxide or a salt, it is necessary to wash the dialkyltin oxide obtained above several times with a large quantity of water, each washing being followed by separation by filtration, centrifugation or other suitable means.
The present inventors believed that the disadvantages of the prior art processes are mainly due to the necessity for filtration or centrifugation. They further believed that if the hydrolysis can be performed such that it results in the formation of three phases, i.e., an intermediate aqueous phase, an upper organic phase and a lower dialkyltin oxide phase, not only each phase can be easily separated from the others without filtration or centrifugation but also the production process can be enclosed in a closed-system completely. They have made intensive studies based on the above and, as a result, completed the present invention.